The present invention relates generally to a closed type battery, and more particularly to a closed type battery comprising a battery can and a battery terminal different in polarity therefrom, which is mounted to the battery can by caulking via an insulating member.
Various batteries are used as power sources for electronic equipments of miniature size, and miniature yet large-capacity closed batteries are employed as power sources for cellular phones, notebook PCs, camcorders, etc. Typically, closed batteries using a non-aqueous electrolyte such as high-capacity lithium batteries and lithium ion rechargeable batteries are now used.
To keep pace with the downsizing of equipments, closed batteries of rectangular shape capable of making effective use of a small space, to say nothing of cylindrical batteries, are widely used. In a typical rectangular battery, a battery can that serves as one electrode of the battery is provided with an electrode terminal while isolated therefrom by an insulating member.
One such typical example of the closed type battery of rectangular shape is shown in FIG. 4.
A closed type battery shown generally at 1 comprises a cylindrical form of rectangular metal package 2 (hereinafter often called the battery can) made of stainless steel, soft steel nickeled on its surface, etc., in which there is a battery element comprising a roll form of cathode and anode stacked one upon another via a separator. At the upper end of the battery can 2, there is a header 7 formed by integrating an external insulating sheet 4A and a cathode-side electrode drawing sheet 5 with a metal sheet 3 by means of a cathode-side electrode leading pin 6; this header 7 is mounted and sealed at the opening of the battery can 2. One portion 8 of the header 7 is made thinner than the rest thereof so as to let an abnormally rising internal pressure escape from the battery and another portion of the header 7 is provided with a hole 9 from which an electrolyte is poured in the battery assembly and which is sealed up after the pouring of the electrolyte. After the electrolyte is poured from the hole 9 into the battery assembly, a metal member such as a stainless steel member is embedded in that hole, and then welded thereto for sealing purposes.
One exemplary header is shown in FIGS. 5(A) and 5(B). FIG. 5(A) is an exploded perspective view of the header, and FIG. 5(B) is illustrative of the header in which an electrode-leading pin is not caulked as yet.
An internal insulating sheet 4B formed of a polypropylene, fluorocarbon resin, etc. is mounted on a metal plate 3 formed of a stainless steel plate, a nickeled soft steel plate, etc. by inserting a projection on the sheet 4B into a through-hole 10 formed in the plate 3 from below. Then, an external insulating sheet 4A is placed over the upper surface of the plate 3 to form an insulating member. Then, an electrode-leading pin 6 formed of a metal of good conductivity such as aluminum or an aluminum alloy and having a collar 6A is inserted through a hollow portion of the projection on the internal insulating sheet 4B, and an electrode-drawing sheet 5 is fitted in the external insulating sheet 4A. Finally, the collar 6A and the tip of a shaft 6B of the electrode-leading pin are caulked from above and below to form a header 7.
After joined to the collar 6a of the electrode lead pin 6 of the thus prepared header 7, an electrically conductive tab 12 joined to the battery element and covered with an insulating member 11 is fitted into an opening at the battery can, and then laser welded at its periphery to seal up the opening.
Upon header assembling, the electrode-leading pin 6 is crushed by caulking into contact with the plane of the electrode-drawing sheet 5, so that a conductive connection is made between the electrode-leading pin and the cathode-drawing sheet 5. On the other hand, the lower surface of the electrode-drawing sheet 5 comes in engagement with the surface of the external insulating sheet 4A to keep air-tightness.
The external insulating sheet 4A, because of having a cylindrical portion 4AT, is kept stable even upon caulking. However, the internal insulating sheet 4B, because of being in a flat sheet form, is urged against the flange 6A of the electrode-leading pin upon caulking, producing force that acts outwardly from the center of the shaft. This in turn may give rise to a void 4C at the junction of the external insulating sheet 4A and the internal insulating sheet 4B, which void may otherwise make the sealing of the battery worse over time.
FIG. 6 is illustrative of another header. FIG. 6 is a sectional view of the header.
The header of FIG. 6 is different from that of FIGS. 5(A) and 5(B) in that an external insulating sheet 4B has a cylindrical portion 4BT.
As an electrode-leading pin 6 is crushed by caulking upon header assembly, a tip 6C of the electrode-leading pin is crushed to urge an electrode-drawing sheet 5, so that a monolithic structure is formed. When the tip 6C of the electrode-leading pin 6 is crushed, however, one end of the electrode-drawing sheet 5 is urged to flip up the other end. This may again result in a void 4D between the electrode-drawing sheet 5 and the external insulting sheet 4A, exercising adverse influences on the sealing properties of the battery as is the case of FIG. 4.